Ah, it wont be the same with sprite_index because it sets the full sprite to the single value only for metal/roughness. The actual sprite colors would come out really weird as metal/roughness. It is possible to try and edit shaders and use like grayscale values, but it will still be a bit odd I think. The material packer that comes with is your best bet at easily making materials for sprites/pixel art, as most workflows for materials are much more in-depth and require full tools for doing so.
Yep.
Since I have multiple sprites that change depending on the player input, everytime the sprite changes, I get the sprite name and add an "_n" then use asset get index to change the normal map to the sprite that is named the same as sprite index with a "_n" after it. I did notice that when I updated the material map in this way (instead of just setting it to sprite index in the variable defs) the result was much closer to the original set up I had with material sprites, but it wasn't exact. I might be able to tweak the metalic/roughness set numbers to get it to where it was.